This invention relates to an optic fiber wavelength multiplexer-demultiplexer, liable to be used as a component in optic fiber teletransmission installations.
We already know such multiplexers-demultiplexers which have been described, then gradually perfected, in particular in the French patents FR-2.543.768, FR-2.519.148, FR-2.479.981, FR-2.496.260 and in the European patent EP-0.196.963.
With optic fiber multiplexer-demultiplexer, we mean devices in which the input and output luminous waves are propagated by optic fibers.
The invention also relates to optic fiber routers in which a variable number of input fluxes, each of a particular wavelength, propagated by spacially distinct optic fibers, are directed to a possibly different number of output fibers.
In these various devices, a dispersing system plays the coupling role, for a given wavelength between an output fiber and an input fiber.
A channel is therefore defined with, of course, a certain spectral width .DELTA..lambda..
The performing multiplexers-demultiplexers or routers must simultaneously enable operation of a large number of channels, each of these channels, centered on a wavelength .lambda., must exhibit a spectral width .DELTA..lambda. as broad as possible, while avoiding any crosstalk.
There is a crosstalk when a portion of the energy generated from a channel is partially mixed to the energy of an adjacent channel. Crosstalk is well-known to disturb communications and the devices exhibiting an excessive level of crosstalk are useless in practice.
To simplify the description, the device according to the invention will be denominated a multiplexer-demultiplexer, whereas we may be dealing with a multiplexer, a demultiplexer or a router.
The purpose of the invention is therefore to suggest a multiplexer-demultiplexer offering improved properties and, while preserving adequate separation of the channels, enhancing the spectral width of each of them.
In order to reach this target, it has been suggested, according to the invention, to implement input or output optic fibers, possibly input as well as output optic fibers, with index variations enabling to broaden the requested spectral width.
In this view, the invention relates to an optic fiber wavelength multiplexer-demultiplexer comprising a dispersing system, at least one input fiber and at least one output fiber, wherein the output fibers have a core and an optic sheath (cladding).